What happened
On February 2, 2019, an AgustaWestland AW139 helicopter with registration 5N-CML, operated by Caverton Helicopters Limited, was conducting a VIP charter flight. The aircraft had departed Abuja for Kabba, Kogi State, carrying the Vice President of the Federal Republic of Nigeria and his entourage, totaling 12 persons on board.
During the approach to the temporary landing site at the Kabba football field, the crew identified the area using dust clouds generated by a preceding police helicopter. The aircraft descended to approximately 50 feet above ground level to enter a hover for landing. At this altitude, the crew encountered a brownout condition caused by rotor downwash kicking up dust from the dry terrain. This phenomenon obscured external visual references, leading to a loss of situational awareness and spatial disorientation.
As the helicopter descended through 15 feet, indicated by radio altitude callouts, it touched down hard on its right main landing gear. The impact caused the aircraft to roll onto its right side. Despite the significant damage to the airframe, including the right horizontal stabilizer and tail rotor blades, all 12 occupants evacuated uninjured.
The investigation
The Accident Investigation Bureau (AIB) examined the flight data recorder, cockpit voice recorder, and wreckage distribution. Key findings included:
- The flight crew had no formal training in brownout conditions at the time of the accident, though the pilot had prior experience with such events.
- The company’s Safety Management System did not require a specific risk assessment for the unapproved landing site prior to dispatch.
- The aircraft's Multi-Purpose Flight Recorder experienced a failure during cruise, but this did not contribute to the accident as per Quick Reference Handbook procedures.
Findings
The investigation determined that the primary causal factor was the encounter with a brownout condition during the hover-to-land phase. This resulted in the loss of external visual cues, spatial disorientation, and misjudgment of ground clearance.
Contributory factors included:
- Inappropriate landing technique: The crew failed to maintain adequate visual references during the critical low-altitude phase.
- Non-adherence to procedures: The flight did not follow company protocols for anticipated brownout conditions.
- Insufficient planning: There was a lack of comprehensive risk assessment and limited preparation of the landing site prior to the flight's commencement.
Safety action
Following the accident, the AIB issued interim and final safety recommendations. The Nigerian Civil Aviation Authority (NCAA) issued an All Operators Letter requiring helicopter operators to establish procedures for handling brownout conditions and to amend training programs to include recognition and recovery techniques. Caverton Helicopters Limited enhanced its simulator training to include brownout scenarios and reviewed its operations manual regarding risk assessments for temporary landing sites.